The invention is related to a disc brake apparatus. And more particularly, the invention is related to a disc brake apparatus adopting a pin slide type referred to as a floating type.
A disc brake apparatus can be classified into a type having a piston only at an inner side of a caliper for pressing a brake pad and a type having pistons at both inner and outer sides thereof.
The former type is a disc brake apparatus referred to as a floating type and has a configuration in which the caliper itself moves in an axial direction of a rotor from a support fixed to a vehicle, which is a basic point. On the other hand, the latter type is a disc brake apparatus referred to as an opposed type and has a configuration in which the caliper itself is fixed and both an inner brake pad and an outer brake pad are directly pressed by pistons provided at the inside.
In the floating-type disc brake apparatus, a pin slide type is adopted regarding the moving of the caliper from the support, in many cases. As an example of the pin slide type, a slide pin is fixed into a through-hole of an arm extending to both a rotation-in side and a rotation-out side of a rotor from a main body of the caliper and the slide pin is inserted and slid relative to a guide hole having a pocket shape formed in a support.
In the disc brake apparatus adopting the above type, a boot made of elastic resin is provided between the slide pin, the guide hole and an entrance, as disclosed in Patent Documents 1 and 2. The boot prevents an impact sound, which is caused due to contact between the slide pin and the guide hole and is referred to as pin rattle, and suppresses drag of a brake pad.    [Patent Document 1] JP-U-6-65632    [Patent Document 2] JP-B-4425737
In the floating-type disc brake apparatus, it is necessary to enable the air to flow into and out of an extra space in the guide hole so as not to disturb the sliding of the slide pin. Therefore, it is general to form the evenness for passing the air on an inner periphery of the boot. However, the boot disclosed in Patent Document 1 blocks an axial end portion of a recess formed on the inner periphery of the boot so as to hold grease in the recess. Due to this, it is difficult for the air to flow through the recess, so that the sliding of the slide pin is disturbed.
Also, according to the boot disclosed in Patent Document 2, the inner periphery through which the slide pin is inserted is formed with a plurality of convex parts so that the convex parts overlap in a stone wall shape (the convex parts overlap with halves thereof being deviated) in an axial direction the slide pin. By this configuration, a concave portion formed between the convex parts configures a recess for passing the air and prevents the slide pin from falling into the recess. However, according to the boot having the configuration, the mold splitting is difficult and the productivity is poor. Also, when a length of a block in an axial direction is lengthened or the number of blocks is increased so as to suppress the elastic deformation of the slide pin in the axial direction, it is necessary to lengthen an entire axial length of an interference part forming the block and also to lengthen an axial length of the boot. As a result, a layout feature of the caliper or support is deteriorated and a processing range (cutting range) of a mount-side is increased to increase the processing cost.